Rducing the pressure on aqueous solutions of polymers



Marcha, A196s M. f. KmER 3,311,114

REDUCING THE PRESSURE 0N AQUEOUS SOLUTIOIIS 0F POLYIERS Filed latch 25, 1965 Me/vin F. Kafg er I BY Imaz... 94m# HTTORNEY REDUCING THE PRISSURE N AQUEGUS SOLUTIONS ,0F POLYMERS Melvin F. Katzer, Damme, Calif., assigner to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Filed Mar. 25, 1965, Ser. No. 442,718

. S Claims. ((1 166-42) The present inventionr concerns maintaining the etlec' tiveuess of polymers in solution. More particularly the invention concerns a method for minimizing the molecular degradative effects of reducing the pressure on a polymer solution.

Occasionally a polymer solution is subjected to a high pressure and in using the solution it becomes necessary to reduce the pressure. Techniques for reducing the pressure Aon fluids, especially lquidskare well known. They kinclude throttlng the liquid through an orifice orr any convenient valve. It has ,been discovered, however, that A.regardless of whether an orilce, nozzle, or adiustable yvalve such as a gate, globe, angle, spiral or pinch valve is used in reducing the pressure on a polymer solution,

"'de'gradation'foi dissolved'polymer results when the pressureof the solution is decreased significantly across the pressure reducing devic'e. This degradation is evidenced by va viscosity loss in the .polymer solution. Degradation of ered that the problem ofmolecular degradation, or viscosity loss, as the result of pressure reduction on a solution of the polymer, can be substantially obviated by ilowing the polymer solution to be depressurized through a liquid permeable, porous-bed vof suicient' length to f achieve a desired pressure reduction. While the invention is not predicated upon any explanation of this effect, it is believed the decrease in the pressure gradient in the direction of solution ow through the porous-bed is responsible for theimproved viscosity retention. p

' The porous-bed may be of consolidated particulate matter such as a sandstone or frits or simply loose particulate solids such as sand, glass beads, linelydivided minerals and the like held in place with suitable retaining means. Porous-beds suitable for use herein can also be prepared as coarse liber plug of materials such as minerals, glass or metal, natural and synthetic polymers and water soluble polyelectrolytes. By high molecular weight is meant one million or more.

The invention is illustrated inthe attached drawings, in which FIGURE l is a sectional elevation of one embodiment of the invention utilizing a porous-bed of consolidated sand, otherwise termed a sand core.

FIGURE 2 is a sectional elevation of a second embodif ment 'of the invention having an adjustable porous-bed of' unconsolidated sand.

' Specifically, the embodiment shown in FIGURE l con. sists of a valve housing 3 in the torm of a cylindrical conduit which has an entering liquid feed line 'I and av t discharge liquid line 8. Sealed within the valve housing 3 amm Patented Mar. 5, 1968 ditions are, of course, satisfied for most applications involvmg aqueous liquids by sandstone. The consolidated sandstone core 5 is held in place within the valve housf the like. For most applications the porous-bed will be at p ing 3 by means of retaining O-rings 13 and 15. These also aid in sealing the core 5 within the valve housing 3 to prevent liquid by-passing of the com 5.

When polymer solution under high pressure is liowed through an assembly such as that shown in FIGURE l, there is a. decrease in the pressure on the polymer solution. At a given liquid tlow rate, the pressure decrease achieved is in proportion to the length of the sandstone core 5. Such pressure reduction is achieved without signif icant loss in the viscosity of the polymer solution. The term viscosity as applied herein to soluble e.g., watersoluble polymers, is considered to be a measure of polymer molecular weight.

The embodiment of the invention shown in FIGURE 2 consists of a housing conduit in which a porous-bed of adjustable length composed of unconsolidated particulate matter occupies a portion of the liquid dow path through the housing. Thus the pressure drop at a given flow rate can be increased or decreased within the limits of the extensibility of the porous-bed.

The illustrated `pressure reducing `rlevicea:consistsfoffa housing conduit 2l in the form of a cylinder with spaced apart inlet ports 23 and 22. Within the interior of the housing conduit 21 is a porousbed, base conduit 25. The inlet end 29 of the base conduit 25 is covered by a porousbed, retaining screen cross member 27. This supports a porous-bed 30. The porous-bed base conduit 25 discharges through the wall of the housing conduit 21 at port 26. At the inlet 29 of the porous-bed base conduit 25 is an extensible sleeve 28.. This slidably engages the outer surface of the porousbcd, base conduit 25. To the extent the brim of sleeve 28 extends above the inlet 29 of the porous-bed, base conduit 25, it provides an adjustable mold form for the porous-bed 30;

The sleeve 28 is moved in or out to adjust the depth of the porous-bed 30 by means of a screw 32 acting through a threaded packing nut 33. The screw 32 is coupled by means of `a rotatable coupling 36 to a yoke 35 which in tarn is fastened to the sleeve 28. The screw 32 is rotated to extend or collapse the porous-bed 30 by means of a Wheel 38. Optionally, any means for achieving linear displacement of the sleeve 28 from without the valve housing conduit 21 can be used. l

The porous-bed 3d within the sleeve 28 is constituted by an unconsolidated, insoluble particulate matter such as silica sand or any other nclydivided material insoluble in the liquid on which prsure is to be reduced. In the valve housing conduit 21 is enough sand 43 to occupy the volume of the porous-bed 30 as delned by the deeve 28, when it is fully extended in relation tofthc porons-bed, base conduit 25. The sand 43 is kept within the valve housing 21 by means of a retaining screen 46.

To operate the described adjustable valve in the preferred manner, it is placed in an upright position, as shown, and the sleeve 28 is extended to provide any desired porons-bed 30 depth. A huid is then passed through the valve assembly entering through port 2.2 and discharging through port 26. The iiuid may be a gas, or a liquid, such as that on which the pressure is to be reduced. This duidl zesthe sand 43 from its position of natural repose in the is a porous-bed in the ferm of a sand core 5 of consoly idated sand, viz., sandstone. The essential requisites ot the porous-bed are insolubility in and permeability to the liquid on which pressure reduction is desired. These cons' e.. 1 l` annulus 40 and, to the extent required, the sand ows into and fills the porous-bed 30 from the 'retaining screen 27 to, or slightly above, the brim of the sleeve 28.

Once the porous-bed 3Q has been established, lluid on which the pressure is to be reduced is owed into the valve housing 21 through port 23. Although good depressurization can.be achieved by continuing the iluid liow.

through port 22, duid entering port 23 enters the valve musing 21 above the level of the sand 43 in the annulus .t is t a 3 e 40 thereby avoiding continuously lluidizing the me. The liquid then ows through the porous-bed 30 of sand and ultimately discharges from the valve through port 26 at a pressure lower than inlet pressure.

-Ifitisdesix'edtotlccreasethepressuredropatacer-y tain ow rate, the sleeve 28 is depressed by turning the vscrew 32. The llow path of the liquid through the porousbedttisdecreasedand, thus, thepressuredropisdrf creased. An alternate mode of operaion achieves a pressure drop across the annular porous-bed 4l. In this method, the liquid to be depressurized enters port 13 and exits at port 22.

An important advantage of the pressure reducing device described above is its adaptability to back llmhing to minimize pressure drop transients due to gradual plugging or settling in the porous-bed 30.

Forinstance,inthepressure redncingdevkeillus` tratedinFIGURBLalluiiwhichmayeitherbeagas or liquid, is tiowed into the valve housing 2l through port 25 and withdrawn through port 22. When sutiicient pressure is applied, complete displacement of the partic- 'Ell ulate matter from the porous-bed 30 is achieved The valve is then ready for re-establishment of the porous-bed I Although the invention was rst designed as a pressure reducing device to carry out the pressure reducing process of the invention, the apparatus shown in FIGURE 2 is function is achieved by feeding liuids of different composition simnlaneously through ports 22 and 23. Whenever the porousbed which may be serving as a lilter or means of mixing lluids becomes plugged, the llter bed y can be reconstituted as described above.

Pressure reduction on a polymer solution, such as can 'be achieved under the invention, is useful in the secondary recovery of oil by ooding an oil bearing formation with 'an aqueous polymer solution. For convenience the polymer solution is made up and` pressurized at a centrally located pumping station. From the central source of supply, the polymer solution is distributed throughout the oil tield through main transmission lines and into a number of injection wells through spur feeder lines. The pressure at a particular injection well head will often desirably be substantially less than the available pressure in the main line.Asa'result, itis'necessary to reduce thepressureon the polymer solution. Manifestly, this pressure reduction can be advantageously accomplished under the invention with degradation of the polymer in solution and thusminimnmlossofabilitytocontrolmohlityoithe injection fluid.

Since the molecular degradation problem is most ag gravated in instances yof high, molecular weight, soluble.

- ,soluble polyelectrolytes such as polyacrylamide, copolymers of acrylamide and acrylic acid, polystyrene sulicmate,

A 0.05 percent by weight solution of an acrylamide polymer having a molecular weight of about 2 million was owed through the bed in a series of increasing how rates which resulted in a corresponding series of increasing pressure drops. The viscosity of the polymer solution was determined before and after passing the solution through the porous-bed.

It was discovered in this manner that at a pressure gradient of 300 lbs/sq. in. per linear foot of sand bed, tire viscosity loss of the polymer solution was only 0.03 centipoise. In this particular porous-bed, a pressure gradient of 1,000 lbs/sq. in. per linear foot caused a viscosity its of 0.16 centipoise.

In further demonstrations of the invention, conducted in a manner similar to that of the foregoing, except that porous-beds of 9 inches, 6 inches, and 3 inches in length were used, it was discovered that molecular degradation. as evidenced by solution viscosity losses, is controlled by the magnitude of the pressure gradient and is essentially independent of bed length, except insofar as this dimension of the bed affects the pressure gradient.

In comparing conventional pressure reducing valves with the invention, it was found that a pressure drop of 300 lbs. per square inch across a l" gate valve induced a viscosity loss in the same polymer solution of about 0.25 centipoise and that pressure drop of 1,000 lbs/sq. in. :cross the same valvecaused a viscosity loss of about 6.45 centpoise.

Benefits similar to those achieved above with aqueous a polymer solutions can also be achieved by reducing the pressure on solutions of polymers in organic solvents over an extended pressure gradient in accordance with the invention. Y

In addition to adjusting the length of the porous bed, the pressure gradient, or pressure change per unit of distance in the direction of ow, can also bc regulated by adjusting the liquid permeability of the porous-bed. For example, by increasing the particle size of matter used for the porous-bed, its permeability is increased and thus the pres 4o sare reduction gradient is decreased. For a given liow rate,

poxyvinytateonel and pam-mylene entre. similarly an polymers soluble in organic solvents such as polystyrene,

n polyvinyl toluene polymethylmethaerylate and the like can be expected to undergo shear vdegradation when subjected to sharp pressure gradients. In general, polymers obtained by the polymerization of monoethyleneically unv saturated monomers to provide essentially linear, soluble polymers are most subject to molecular degradation as a result of large pressure gradients.

By way of specifically illustrating the invention, a 1.25 inch, schedule 80 steel pipe l2 inches long was packed i ywith silica sand to form a liquid permeable porous-bed. Stainless steel retainer screens were rigidly secured in froutandinbackoftheporous-bed.

the pressure reduction gradient is also decreased by increasing the cross sectional area of the porous-bed. It is preferred to keep the pressure reduction gradient below about i200 lbs. per square inch per linear foot in any particular porous-bed. In any event, the lower the pressure gradient through the porous-bed, the less polymer degradation occurs.

What is claimed is:

` 1. A method for significantly reducing the pressure on a solution of a high molecular weight, essentially linear polymer with minimal molecular degradation of the polyner which comprises owing the polymer solution under pressure through a porous-bed contained within a conduit, said porous-bed being insoluble in, and permeable to, the

a, polymer solution to achieve the desired pressure reduc- 2. A method for significantly reducing the pressure on a solution of a high molecular weight, essentially linear polymer, with minimal molecular degradation of the polymer, which comprises tlowing tbe solution under pressure through a porous-bed contained within a conduit, said porous-bed being at least three inches long, insoluble in,

and permeable t0, the solution at a ow rate such that the pressure reduction gradient inthe direction of liow is less than about 1200 lbs/square inch per linear foot of the porous-bed.

3. A method for signilicantly reducing to a desired level the pressure on a solution of a high molecular weight, essentially linear polymer, with minimal molecular degradation oi the polymer, which comprises llowing the solution under pressure through a porous-bed insoluble in, and permeable to, the polymer solution and increasing the kngth of the porous-bed until the pressure is reduced to tie desired level.

4. In a method for distributing a solution of a high molecular weight essentially linear polymer to oil eld injection wells, which comprises owing the polymer solu tion from a pressurized source of supply into the injection well at a lowered pressure, the improvement which consists in llowing the polymer solution under pressure through a porous-bed contained within a conduit, said porous-bed being insoluble in, and permeable to, the polymer solution to achieve the desired pressure reduction.

5. In a method for distributing a solution of a high molecular weight essentially linear polymer to oil leld injection wells, which comprises tlowing the polymer solution from a pressurized source of supply into an injection well at a lowered pressure, the improvement which consists in llowiug the polymer solution under pressure through a porous-bed contained within a conduit, said porous-bed being insoluble in, and permeable to, the solution at a ow rate such that the pressure reduction gradient in the direction of ow is less than about 1200 lbs/square y inch per linear foot of the porous-bed.

References Cited UNITED STATES PATENTS 2,842,492 1/19ss 5- 3,016,504 2/1963 3,116,191 1/1964 3,180,410 4/1965 3,208,518 9/196s 3,306,356 2/1961 1,140,420 s/191s 10 2,366,036 12/1944 2,815,889 12/1951 2,924,211 2/1960 3,104,115 9/1963 l5 3,104,116 9/1963 3,134,436 s/1964 3,193,011 A1/19611 Englehardt et al.

STEPHEN J. NOVOSAD, Primary Examiner. 2 ALAN COHAN, Examiner. 

1. A METHOD FOR SIGNIFICANTLY REDUCING THE PRESSURE ON A SOLUTION OF A HIGH MOLECULAR WEIGHT, ESSENTIALLY LINEAR POLYMER WITH MIMIMAL MOLECULAR DEGRADATION OF THE POLYMER WHICH COMPRISES FLOWING THE POLYMER SOLUTION UNDER PRESSURE THROUGH A POROUS-BED CONTAINED WITHIN A CONDUIT, SAID POROUS-BED BEIGN INSOLUBLE IN, AND PERMEABLE TO, THE POLYMER SOLUTION TO ACHIEVE THE DESIRED PRESSURE REDUCTION. 